title: Tissue-specific effects of hypothyroidism on postnatal muscle development in the barnacle goose.
abstract: The hypothesis that tissue-specific levels of thyroid hormones may be required for normal locomotor muscle development was investigated in the barnacle goose Branta leucopsis. Hypothyroidism was induced in goslings by treatment with methimazole from either 3 days or 2 weeks of age, and birds were killed at 7 weeks of age. The masses of the pectoralis, iliofibularis, semimembranosus and cardiac ventricle muscles were measured, and samples from these tissues were analysed for the mass-specific activity of the mitochondrial enzyme citrate synthase (CS). An ultrastructural electron micrograph analysis of the pectoralis was also carried out. No significant differences were found between the two hypothyroid groups except for the effect on the relative mass of the iliofibularis muscle. Developmental responses to hypothyroidism were found to be tissue-specific. Hypothyroidism resulted in a significantly lower relative cardiac ventricle mass (by 17 %) and CS activity of the leg muscles (by 34 %), while absolute leg muscle mass was not affected. The relative mass of the pectoralis was significantly lower (by 57 %) in hypothyroid birds and showed a significant, uniformly lower CS activity (by 60-83 %) as a result of a lower mitochondrial fractional volume. Haematocrit and capillary-to-fibre ratio in the pectoralis were also significantly lower in hypothyroid birds, and skeletal growth and plumage development were affected.
authors.affiliation: School of Biological Sciences, University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: K E
authors.initials: KE
authors.lastname: Deaton
authors.forename: C M
authors.initials: CM
authors.lastname: Bishop
authors.forename: P J
authors.initials: PJ
authors.lastname: Butler
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000097:blood / Q000254:growth & development* / Q000502:physiology; D015992:Body Mass Index; D001846:Bone Development; D002950:Citrate (si)-Synthase / Q000378:metabolism; D005241:Feathers / Q000254:growth & development; D005777:Geese; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D007037:Hypothyroidism / Q000139:chemically induced / Q000201:enzymology / Q000503:physiopathology*; D007866:Leg; D024510:Muscle Development; D009132:Muscles / Q000201:enzymology / Q000503:physiopathology; D009928:Organ Specificity / Q000502:physiology; D010369:Pectoralis Muscles / Q000254:growth & development / Q000648:ultrastructure; D013963:Thyroid Hormones / Q000097:blood
chemical_list: D006454:Hemoglobins; D013963:Thyroid Hormones; D002950:Citrate (si)-Synthase